1. Field of the Invention
The present invention pertains to the field of television signal processing. More particularly, this invention relates to selecting the amount of anti-ghosting filtering to be performed.
2. Background
Television transmission signals typically account for a vertical blanking interval (VBI). The VBI refers to the time required by the electron gun in a conventional television set (or similar visual display) to reset itself to the top of the television screen from the bottom of the screen. Conventional television sets and many other visual displays generate their display by using an electron gun(s) to illuminate each line on the television screen. The electron gun illuminates a single line at a time and typically starts at the top of the screen, illuminates every other line as it travels down the screen, then resets itself to the top of the screen once it reaches the bottom. During this reset from the bottom of the screen to the top of the screen, no lines of the screen are being illuminated. This period of reset is referred to as the VBI.
During the VBI, no video information is transmitted by a broadcasting device because the electron gun is not illuminating lines at that time. Thus, control information and/or other data can be transmitted during the VBI rather than video and/or audio information without disrupting the video and/or audio transmission. Typically, a portion of the VBI is used by television broadcasters for control information necessary for displaying the audio and video information. This control information includes, for example, vertical and horizontal video synchronization signals. In addition, a portion of the VBI is typically reserved for broadcasting the text for closed captioning for the hearing impaired. However, unused space remains in the VBI which can be used by a broadcaster to broadcast any of a wide variety of data, typically referred to as teletext data, of the broadcaster's choosing.
One problem inherent in the transmission of television signals is referred to as "ghosting". Ghosting results from an echo(es) of the transmitted signal. Ghosting occurs when there is a reflection of a television signal or similar "bouncing" of the signal off of a particular object in or near the signal's path. Ghosting presents a problem when transferring data over the VBI because the reflected or echoed signal(s) interferes with the data being transmitted.
Several anti-ghosting mechanisms have been developed to reduce the effects of ghosting in a television transmission signal. Two such mechanisms are referred to as Adaptive Baseband Equalization (ABBE) filtering and Lookup Table (LUT) filtering. Both of these anti-ghosting filtering mechanisms look at one or more surrounding samples for a particular sample of data and perform various filtering processes using these bits to reduce the ghosting effects on the signal being transferred.
Using the ABBE and LUT filters reduces the ghosting effects on the signal being transmitted, thereby increasing the quality of the signal. Using these filters, however, requires additional computational time. That is, the system receiving the signals must expend additional computational resources, and therefore time, to perform the filtering; without the filtering, this time could be spent performing other tasks. In situations where the ghosting effects on the signal are not too great, all of the possible filtering which can be done by the ABBE and LUT filters may not be necessary. In these situations, it would be advantageous if computational resources could be freed to perform other more important tasks. Therefore, it would be beneficial to provide a mechanism for automatically selecting how much filtering be done to reduce anti-ghosting effects.
Furthermore, the quality of the signal being transmitted can improve or worsen over time. Therefore, the anti-ghosting filtering procedures selected at is one point in time may become unnecessary, or alternatively insufficient, at a later point in time. Thus, it would be beneficial to provide a mechanism for modifying, in real-time, the selected anti-ghosting filtering to be performed.
As will be described in more detail below, the present invention provides a mechanism for adaptive selection of anti-ghosting filtering to achieve these and other desired results which will be apparent to those skilled in the art from the description that follows.